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In this work, the effect of silica particle size and organosilane type used in the silica organofunctionalization on the thermal and mechanical properties of high-density polyethylene (HDPE)/silica composites were evaluated. HDPE/silica composites were prepared by the extrusion method using two types of silica: fumed silica, with nanometric particle size and silica gel, micrometric, modified with organosilanes containing methyl or octyl functional groups. Silicas were added to the HDPE at 1% v/v concentration. The addition of the silicas to the HDPE did not influence the melt (Tm) and the crystallization (Tc) temperatures of the resulting composites but influenced its crystallinity. The mechanical property of Izod impact strength, the dynamic-mechanical rheological test (DMTA) and the surface contact angle analysis showed improvements in relation to pure HDPE when used methyl-modified pyrogenic silica as filler. This result suggests that the surface modification of pyrogenic silica with methylsilane groups results in a stronger interaction of this silica with the HDPE matrix. This effect was not observed for micron-sized silica gel, where modification with organosilanes was not sufficient to guarantee interfacial interaction with the HDPE matrix. [ABSTRACT FROM AUTHOR]

This paper reports the main results concerning the synthesis and characterization of methylsilane and octylsilane-modified silicas. The modification of the silicas with these groups aims to make the silica surface hydrophobic and thus compatible with high-density polyethylene (HDPE) in HDPE/silica composites. In the present work, two types of silica were organofunctionalized: a pyrogenic silica and a silica gel. The silicas were characterized by a series of complementary techniques with the objective of investigating the nature of the surface species and their textural and morphological characteristics. The SEM images showed that the modification of the silicas with organosilanes has been not resulted in changes on the morphology and on the size of silica particles. In relation to the texture properties, determined by N2 adsorption-desorption porosimetry, the silica modification resulted in a decrease of the specific area (SBET) and the mean pore volume, a behavior attributed to the partial coverage of the adsorption sites by the organosilane molecules. The TGA analysis showed that both the methylsilane groups and the octylsilane groups on the surface of silica and silica gel are thermally stable up to 200 ° C, which enables the organofunctionalized silicas in terms of thermal stability, for the process of preparing the composites by extrusion. The results of applying these organofunctionalized silicas in the development of HDPE/silica composites will be presented in a subsequent article, part II of this research. [ABSTRACT FROM AUTHOR]

According to IUPAC, the composites are multicomponent materials comprising multiple, different (nongaseous) phase domains in which at least one type of phase domain is a continuous phase. High density polyethylene (HDPE) reinforced with silica particles is an example of a composite material. Diatomite is a natural silica commonly used in filter media. In the present work, the diatomite was organofunctionalized with methyltriethoxysilane (C1) and then used in the preparation of HDPE/diatomite composites with diatomite content of 2.0 and 5.0 wt%. The composites were evaluated in terms of mechanical properties by dynamicmechanical analysis (DMTA), Izod impact test and flexural strength and tensile strength tests. The Fourier transform infrared spectrum (FTIR) of the organofunctionalized diatomite presented bands characteristic of methyl groups, proving the efficiency of the surface modification. The addition of 5.0% diatomite in HDPE resulted in an increase of 8.0 °C in thermal stability, crystallinity (72 to 78%) and in approximately 4.0% in the storage modulus (G'), compared to pure HDPE.SEM analyzes showed the presence of diatomite agglomerates in the HDPE matrix. The Izod impact strength of the composites for this composite was 50 J / m, half of that observed for pure HDPE. The properties of tensile strength were not influenced by the presence of diatomite in HDPE. [ABSTRACT FROM AUTHOR]